The invention is in the field of diagnosing lesion severity of a lesion in an arterial lumen of a human subject.
Stroke volume pumping by a left ventricle into its adjacent proximal aortic root causes the pressure of the root segment to rise and its wall to distend because it is already filled with blood, thereby creating a high pressure wave which is transmitted into the arteries. The morphology of the aortic pressure waveform corresponds to the three phases of the pressure pulse as follows: Phase I is known as the anacrotic rise occurring during early systole and correlating with the inotropic component, the gradient, and height of the anacrotic rise, and anacrotic notch being related to the rate of acceleration of blood. Phase II appears as a rounded shoulder by virtue of the continued ejection of stroke volume from the left ventricle, displacement of blood, and distension of the arterial walls which produce the rounded appearance. And Phase III appears as a descending limb due to diastolic run-off of blood. This part of the curve normally begins with a dicrotic notch as effected by blood running against the closing aortic valve separating systole from diastole.
A decrease in arterial distensibility occurs with aging and in hypertension, but is most apparent in generalized arteriosclerosis. A decrease in arterial distensibility causes an increase in pulse wave velocity which in turn results in the early return of reflected waves from peripheral sites. These reflected waves fuse with the systolic part of the pulse, leading to increases in pulse pressure, to a late systolic peak in the pulse waveform and disappearance of the diastolic wave, and in particular the dicrotic notch.
Early observations suggested that pressure waveform analysis is useful in evaluating the severity of atherosclerotic vascular disease. Using a classification according to the appearance of the dicrotic notch in the peripheral pressure waveform, it was demonstrated that abnormal pressure waveform with the absence of discrete dicrotic notch is associated with significant atherosclerotic vascular disease. Dawber, T. R., et al, xe2x80x9cCharacteristics of the dicrotic notch of the arterial pulse wave in coronary heart diseasexe2x80x9d, Angiology, 1973, 24(4): p. 244-55.
More recently, it was shown that abnormalities in the carotid pulse waveform with alteration or disappearance of the dicrotic notch is highly correlated with isolated aortic stenosis. O""Boyle, M. K., et al, xe2x80x9cDuplex sonography of the carotid arteries in patients with isolated aortic stenosis: imaging findings and relation to severity of stenosisxe2x80x9d, American Journal of Roentgenology, 1996, 166(1): p. 197-202. Cousins, A. L., et al xe2x80x9cPrediction of aortic valvular area and gradient by noninvasive techniquesxe2x80x9d, American Heart Journal, 1978, 95(3): p. 308-15.
Furthermore, the absence of the dicrotic notch in the pulse pressure waveform distally to aortoliac disease was almost always associated with significant proximal artery stenosis whereas its presence was found as an excellent index of normal hemodynamics. Barringer, M., et al., xe2x80x9cThe diagnosis of aortoiliac disease. A noninvasive femoral cuff techniquexe2x80x9d, Annals of Surgery, 1983, 197(2): p. 204-9.
In accordance with the present invention, there is provided apparatus for diagnosing lesion severity of a lesion in an arterial lumen supplying blood to a muscle in its non-hyperemic state of a human subject, the apparatus comprising:
(a) an intravascular pressure measurement device for deployment adjacent the lesion in the arterial lumen supplying blood to the muscle in its non-hyperemic state;
(b) a pressure monitoring system connected to said intravascular pressure measurement device for measuring a non-hyperemic pressure waveform acquisitioned proximal to the lesion, and a non-hyperemic pressure waveform acquisitioned distal thereto, the former consisting of a series of pressure pulses each including a dicrotic notch, and the latter consisting of a series of pressure pulses each potentially including a dicrotic notch depending on the severity of the lesion; and
(c) a Pulse Transmission Coefficient (PTC) processor for processing information relating to the shape of the dicrotic notch of at least one pressure pulse of said proximal non-hyperemic pressure waveform and either the absence of dicrotic notches along said distal non-hyperemic pressure waveform or the shape of the dicrotic notch of at least one pressure pulse of said distal non-hyperemic pressure waveform if present to calculate the value of a PTC parameter indicative of the severity of the lesion.
The present invention is based on the clinical findings that the absence or continuing presence of a dicrotic notch distal to a lesion in an arterial lumen supplying blood to a muscle in its non-hyperemic state significantly correlates to the myocardial fractional flow reserve (FFR) parameter in those instances in which FFR is typically employed to physiologically assess lesion severity but without the need for inducing hyperemia in the muscle as is required for currently employed parameters for physiologically assessing lesion severity, for example, FFR, coronary flow reserve (CFR), and others. On the basis of these findings, the present invention proposes a new parameter for incorporation in blood pressure monitoring apparatus, for example, the SmartFlow(trademark) apparatus commercially available from Florence Medical Ltd, Kfar Saba, Israel, for facilitating the decision making process alongside parameters such as FFR, CFR, and others to determine the necessity of medical treatment of a lesion, and the type of such treatment.
In actual fact, the present invention proposes two alternative parameters PTC(E) and PTC(A) pertaining to different but related characteristics of dicrotic notches. In particular, PTC(E)=Edistal/Eproximal where Edistal is the energy of the high frequency component of the dicrotic notch of a pressure pulse of a human subject""s distal non-hyperemic pressure waveform and Eproximal is the energy of the high frequency component of the dicrotic notch of a pressure pulse of his proximal non-hyperemic pressure waveform. While PTC(A)=Adistal/Aproximal where Adistal is the area of a dicrotic notch of a pressure pulse of a human subject""s distal non-hyperemic pressure waveform and Aproximal is the area of a dicrotic notch of a pressure pulse of his proximal non-hyperemic pressure waveform. The present invention is suitable for determining lesion severity of lesions in coronary arteries, renal arteries, iliac arteries, carotid arteries, and other arterial lumens.